Esprit S4s oil temperature gauge retrofit instructions

[tomcattom]

Having now successfully fitted and tested my oil temperature gauge in replacement of the dashboard clock on my S4s I thought I would share the necessary steps in one place for anyone else that wants to do it.

There are several ways you can do this modification, but I’ve documented what I felt what the cheapest approach. The wiring modifications have been done without butchering the original loom so that the clock could be restored should I want to in the future. You could cut into the loom and solder things together if you want to reduce the cost further, but I personally think that is a false economy.

What you need to do the modification

 

• 52mm oil temperature gauge and matching sensor with M10 thread
  • I used a Lotus branded VDO gauge A082N6067F. It seems there are two different styles of face used on the VDO oil temperature gauge with both using the same part number, I went for a secondhand one dated from 1989 because it looked like it matched the rest of the CAI gauges already in the car more closely
  • The required Lotus sensor part number is A082N6068F
  • x1 red 286 bulb if you want the gauge illumination to match the rest of the gauges
• M10 sensor T-piece. I used this one from Merlin Motorsport: https://www.merlinmotorsport.co.uk/p/oil-pressure-gauge-t-piece-m10-x-1-mse050m
• Wiring – You can used any 1mm thin wall colour you like, but the lengths and colours below follow the colours Lotus use in the wiring diagram.
  • Yellow/Black – about 100cm
  • Black – about 10cm
  • Green – about 20cm
• Connectors/crimps – The items in bold are required to connect into the existing loom wiring, the others are specific for connection to the VDO gauge and may vary if you use a different gauge and sensor.
  • x1 Econoseal male connector terminal (926981-2) - https://cpc.farnell.com/amp-te-connectivity/926981-2/crimp-pin-econoseal-0-5-1mm/dp/CN13393
  • x1 Econoseal green wire weatherproofing seal (281934-4) - https://cpc.farnell.com/amp-te-connectivity/281934-4/wire-seal-green/dp/CN13747
  • x1 Lucas Rists male connector terminal. I have been unable to find a part number, let alone a source of these, so I bought a section of dashboard loom from a breaker and robbed a terminal and length of wire out of that. I have plenty of spare crimps left so if anyone wants one to do this drop me a DM and I’ll happily chuck one in the post for you to save buying a whole loom.
  • x3 6.3mm female spade connector crimp and insulation boot for making the connections to the back of the gauge
  • x1 4.8mm female piggyback spade connector crimp and insulation boot
  • x1 4.8mm male spade connector crimp and insulation boot.
  • x2 2.8mm female spade connector crimps WITHOUT insulation boot for modifying the gauge illumination circuit
  • 501 bulb conversion loom

Engine bay sensors and wiring changes

1. Disconnect the battery

2. Remove the starter motor to gain access to the existing oil pressure sensors.

3. Disconnect and remove the oil pressure sensor transducer and low pressure warning switch. The transducer shown below is wrong and so you shoudn't find all the adapters fitted that I had if the OE transducer is fitted.

4. Install the sensor T-piece into the port on the right where the oil pressure gauge transducer was removed and install the oil pressure transducer, low pressure switch and temperature sensor as shown using thread sealer on all the threads. In my case I had to orient the side port on the T-piece at the 6 o’clock position, however if you are running an electric charge cooler pump I think it would be better to orient that port at the 12 o’clock position because there is more space there. With the pressure switch at the 6 o'clock position it will *just* clear the starter, but it is very tight. I also used a 10mm copper washer on the low pressure switch because otherwise it was partially obscuring the flow of oil to the pressure transducer. The copper washers aren't required on the transducer shown here if using the OE transducer.

5. Under the coolant header tank locate the round three pin connector for the oil sensor sub harness (shown disconnected in this photo), disconnect it and remove the sub harness from the car. There should be three wires going into one side of the connector (main body loom side) and only two on the other side (sub harness side).

6. Remove the nylon balnking pin from the back of the round three way connector on the sub harness. Remove the wire seal from the hole if it doesn’t come out with the nylon blanking pin.

7. Fit the Econoseal terminal and green weather seal to the yellow/black wire and fit it into the unused way on the connector

8. Now take the loom back to the car and plug it back in and cut the yellow/black wire to the desired length to reach the oil temperature sensor

9. Remove the sub harness again and feed the wiring into the protective tubing and then fit a 6.3mm female spade crimp and insulation boot to the loose end. You’ll need to cut a small slot in the insulation boot so it can fit on to the sensor.

12. Return the sub harness to the car and wire it into the three oil sensors as follows and re-fit the starter motor.

• Yellow/Black = oil temperature
• Brown/White = low oil pressure switch
• White/Brown = oil pressure gauge transducer

 

Gauge installation and binnacle wiring alterations

These steps may vary depending upon whether you use the VDO gauge as I did or an alternative. The steps should be largely the same but the types of connector used could be different.

1. Remove the dashboard binnacle cover

2. Remove the bulb holder and purple and black wires from the back of the clock. The purple wire is a permanent live for the clock to retain time and we won’t need this for the oil temperature gauge so tape this out of the way safely to prevent it shorting on anything.

3. Remove the clock from the dashboard and install the oil temperature gauge in its place

4. Take the remains of the Yellow/Black wire and cut about a 30cm length and fit the male Lucas Rists connector terminal to one end and a 6.3mm female spade connector terminal and insulation boot to the other end

5. Install the rists connector in the smaller of the two large harness adapters in the binnacle in the position shown and connect the other end to the terminal labelled ‘G’ on the back of the VDO gauge. You'll need to slide the yellow strain relief clip off the connector to install the terminal.

6. To connect power to the gauge take a 20cm length of green wire and fit the 4.8mm piggyback crimp and insulation boot on one end and a 6.3mm female spade crimp and insulation boot on the other end.

7. Remove the green supply wire from the boost gauge and connect the piggy back connector to the boost gauge and reconnect the supply to the boost gauge. Connect the other end of the piggyback wire to the ‘+’ connector on the back of the VDO gauge.

8. To connect the earth to the gauge you’ll need to make up a little adapter loom because the VDO gauges use a 6.3mm spade connection and the loom has a smaller 4.8mm connection to fit the standard CAI gauge. I used a 10cm length of black wire with a 4.8mm male spade connector and boot on one end and a 6.3mm female connector with boot on the other end. Plug this into the earth disconnected from the clock and plug the other end in the ‘-‘ connections on the back of the VDO gauge.

9. Finally to sort the illumination take the 501 harness adapter and crimp a 2.8mm female spade connectors onto each of the wires on the harness adapter and plug it into the bulb holder on the VDO gauge and plug the other end into the original bulb holder that you removed from the clock.

10. With everything wired in you should have an arrangement that resembles this

 

 

You should now now be able to reconnect the battery and test that your oil temperature gauge works as expected. It will probably take about five to ten minutes of running before the gauge registers any oil temperature.

 

[Chillidoggy]

Excellent work, Tom.

[EXCEL V8]

Thread revival!  Does anyone know if the same sensor works with the 30-130 gauge (as above) as well as the 50-140 gauge that SJ sells?  I have two 30-130 gauges that I would like to use.

Thanks

Pete

[naasaa]

There is no oil flow where you fitted that sensor, so it cant read the oil temperature!

[tomcattom]

How do you figure that @naasaa 😕

It's placed right below the turbo oil feed hose for a start and second it's as per the factory oil temperature sensor location on the earlier S4.

[naasaa]

7 hours ago, tomcattom said:

How do you figure that @naasaa 😕

It's placed right below the turbo oil feed hose for a start and second it's as per the factory oil temperature sensor location on the earlier S4.

My apology. Missed to see that you switched location with the low oil pressure switch. Just saw it as you located it below the oil pressure transducer.